Conventionally, there is a well-known working vehicle called as a skid steer loader, which can turn on a small circle with driving wheels by operating steering levers provided in an operation control portion so as to carry out loading and dumping work in a limited space. Generally, the skid steer loader is equipped on a side portion thereof with a lift arm, which is formed in an approximate inverse L-shape in a side view, and extended forward from a rear portion of the vehicle. The lift arm can lift up and down a working machine, such as a bucket, attached on a front end of the arm, in the almost vertical direction relative to the ground.
Such a skid steer loader is desired to have a sufficiently long bucket reach when the lift arm is lifted up at an uppermost position. To achieve this request, the vehicle requires a bracket to support the lift arm. The bracket tends to be a big structure so as to have enough strength. A bigger bracket is needed for a longer bucket reach. However, a big bracket sometimes obstructs an operator's rear or side view from the operation control portion so badly that the operator feels difficulty in backing and turning operation of the vehicle.
To solve the above problem, a conventional type skid steer loader is disclosed in JP-Hei6(1994)-33476, in which the operator's side view is improved without increasing the number of needed links.
However, in each of the conventional skid steer loaders, the lift arm, while being lifted up, moves away from the vehicle body so as to have a bad influence on the skid steer loader in its fore-and-aft balance and its loading and dumping work, because the arm is integrally formed between its ends pivoted onto the bracket and the working machine, so as to have a constant angle bend.
Besides, JP-Hei11(1999)-158905 discloses a conventional art relating to a skid steer loader, in which an operator doesn't have to move the vehicle back and forth so much in dumping stuff loaded on a bucket onto a truck etc. Furthermore, according to the document, some other problems are also solved to improve operability of loading and dumping work. For example, the vehicle is prevented from lurching backward when the bucket is being lifted up.
However, the above conventional skid steer loader is configured in such a way that the bucket is positioned at the forefront of the vehicle when the lift arm is lifted up at an uppermost position. Therefore, the vehicle tends to lose balance in dumping stuff loaded on the bucket onto a truck etc.
JP-2001-64990 discloses a skid steer loader which is equipped with a slidable arm on a main arm of a lift arm. The slidable arm is slidable against the main arm so that a bucket provided thereon should move on a demanded locus, such as a vertical line, a circular arc, etc. in loading and dumping work.
However, the above-described skid steer loader has a complex mechanism and is expensive in exchange for having a desired bucket locus because it needs additional elements, such as sensors for detecting a distance slid by the slidable arm and a tilt angle of the bucket, controllers for controlling the lift arm on the basis of detection values, and several control valves.
In view of the above-described problems, the present invention aims for providing a skid steer loader which secures a wide rear and side view field for an operator in an operation control portion, and which keeps stable balance even when a lift arm is lifted up at an uppermost position. The present invention also aims for providing a simple mechanism for lifting up the lift arm keeping an opening of a bucket face almost upward.